Embodiments of the present specification relate generally to diagnostic imaging systems, and more particularly to systems and methods for autofocusing a digital microscope via use of optical coherence tomography (OCT).
Digital optical microscopes are used to observe a wide variety of samples such as biological tissues on histopathologic slides for archiving, telepathology, and/or rapid information retrieval. Generally, the digital microscopes may include high resolution objective lenses having small depths of focus to aid in generation of sharp images corresponding to a target region in a selected sample. However, such a tight depth of focus necessitates that the target region be closely aligned to a focal point of an associated objective lens.
Accordingly, in a conventional digital microscope, the sample may be repeatedly repositioned along an axial Z dimension to focus and/or locate an optimal imaging position. Specifically, the conventional microscope may perform autofocusing by obtaining multiple images at multiple focal distances, determining quantitative characteristics for each image, determining an optimal focal distance based on the quantitative characteristic, and using a feedback loop to adjust the focal distance for imaging the target region.
However, such repeated repositioning of the sample and/or a multiple image acquisitions may create time delays that prevent rapid autofocusing during diagnostic procedures. For example, a biomarker multiplexing process may entail tissue preparation, staining, bleaching, and/or imaging the target region for determining relevant clinical indicators. Although, the tissue preparation, staining, and bleaching may be batch-processed, slide scanning based on fluorescence imaging still remains a bottleneck on an overall processing time, thus impeding expedited and/or real-time diagnosis and/or treatment of a patient. Similarly, an inability to rapidly autofocus may also impede other automated biological and biomedical applications such as high-throughput pharmaceutical screening and/or large-scale autonomous cell manipulation. An inability to accurately autofocus may also hinder performance of non-medical imaging applications such as integrated circuit chip inspection and/or microassembly of hybrid microelectromechanical systems (MEMS).
Accordingly, certain conventional digital microscopes employ laser-based focusing systems for automatically focusing on the target region. Specifically, the laser-based auto-focusing systems perform autofocusing by directing a laser beam at the sample, measuring a reflection of the laser beam off the sample to provide a single reference point, and using a feedback loop to adjust the focal distance. Although the laser-based focusing approach provides autofocusing, the single reference point may lack sufficient information for accurate autofocusing. Particularly, the laser-based focusing approach may merely provide sufficient information to locate glass interfaces such as the coverslip and slide below. However, when using the laser-based focusing approach, the sample itself may provide only a weak and non-repeatable signal that may not be sufficient to determine an accurate location of the sample even when using a known offset from the coverslip or slide to the sample.